This application relates generally to receiver circuits and, in particular to a CATV tuner with a frequency plan and architecture that allows the entire receiver, including the filters, to be integrated onto a single integrated circuit.
Radio receivers, or tuners, are widely used in applications requiring the reception of electromagnetic energy. Applications can include broadcast receivers such as radio and television, set top boxes for cable television, receivers in local area networks, test and measurement equipment, radar receivers, air traffic control receivers, and microwave communication links among others. Transmission of the electromagnetic energy may be over a transmission line or by electromagnetic radio waves.
The design of a receiver is one of the most complex design tasks in electrical engineering. In the current state of the art, there are many design criteria that must be considered to produce a working radio receiver. Tradeoffs in the design""s performance are often utilized to achieve a given objective. There are a multitude of performance characteristics that must be considered in designing the receiver. However, certain performance characteristics are common to all receivers. Distortion and noise are two such parameters. The process of capturing the signal creates distortion that must be accounted for in the design of the radio receiver. Once a radio signal is captured, the noise surrounding the received signal in the receiver must be considered. Radio signals are often extremely weak and if noise is present in the circuit, the signal, even though satisfactorily received, can be easily lost in this noise floor. The current state of the art in receiver design is often directed to overcoming these receiver limitations in a cost effective manner.
There is therefore provided in a present embodiment of the invention a method for tuning filters. First a dummy filter is stimulated with a frequency that is available locally Next the dummy filter is tuned to its designed center frequency. This is done by switching in capacitors to shift the filter response curve down in frequency. Next the capacitor values required to center the response of the actual filter to its designed center frequency are determined by using frequency scaling a ratio of the dummy filter""s required capacitance to the actual filter""s. The required capacitance is added simultaneously with the dummy filter""s capacitance. Tuning stops when the dummy filter""s response is centered about its tuning frequency. Next the tuning circuitry is disengaged.
Many of the attendant features of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description considered in connection with the accompanying drawings, in which like reference symbols designate like parts throughout.